According to the developments in optical measurement techniques in recent years, detection and/or measurement of faint light at a single photon or single fluorescent molecule level have become possible by using an optical system of a confocal microscope and a super high sensitive light detection technique capable of the photon counting (single photon detection). Thus, there are variously proposed optical analysis techniques of performing detection of a characteristic, an intermolecular interaction, a binding or dissociating reaction of a biological molecule, etc. by means of such a faint light measurement technique. As such optical analysis techniques, for example, there are known Fluorescence Correlation Spectroscopy (FCS, see e.g. patent documents 1-3 and non-patent documents 1-3), Fluorescence Intensity Distribution Analysis (FIDA, e.g. patent document 4, non-patent document 4) and Photon Counting Histogram (PCH, e.g. patent document 5). In addition, in patent documents 6-8, there are proposed methods of detecting fluorescent substances based on a time progress of fluorescence signals of a sample solution measured using the optical system of a confocal microscope.
Furthermore, in patent documents 9-11, Applicant of the present application has proposed a novel optical analysis technique, using an optical system which is capable of detecting the light from a micro region in a solution, such as an optical system of a confocal microscope or a multiphoton microscope, and employing a different principle from optical analysis techniques, such as FCS and FIDA. In the case of optical analysis techniques, such as the above-mentioned FCS, FIDA, the light intensity data obtained by continuously measuring lights from fluorescence molecules floating in a micro region, in which light is detected, in a sample solution (hereafter, called a “light detection region”) is analyzed through calculation processing which computes statistical fluctuations, and thereby a concentration and/or other characteristics of fluorescence molecules are detected. On the other hand, in the new optical analysis technique proposed in patent documents 9-11, the position of a light detection region is moved in a sample solution (i.e., the inside of the sample solution is scanned with the light detection region), and when the light detection region encompasses a light-emitting particle being dispersed and moving at random in the sample solution, the light emitted from the light-emitting particle is individually detected, and thereby each of the light-emitting particles in the sample solution is detected individually so that it becomes possible to perform the counting of light-emitting particles and the acquisition of the information about the concentration or number density of the light-emitting particle in the sample solution. According to this new optical analysis technique (called the “scanning molecule counting method”, hereafter.), not only the sample amount necessary for measurement may be very small (for example, about several 10 μL) and the measuring time is short similarly to optical analysis techniques, such as FCS and FIDA, but also, it becomes possible to detect the presence of a light-emitting particle and quantitatively detect its characteristic, such as a concentration, a number density, etc., at a lower concentration or number density, as compared with the cases of optical analysis techniques, such as FCS and FIDA.
Thus, the “scanning molecule counting method” is expected to be a strong tool enabling an experiment or a test at low cost and/or more quickly than conventional biochemical methods, and also enabling the detection of a concentration and/or a characteristic of a particle of a lower concentration at which FCS, FIDA, etc. cannot be acceptably performed, especially in conducting an analysis of a rare or expensive sample often used in the field of the medical or biological research and development or in conducting tests of a large number of specimens, such as sick clinical diagnosis or the screening of bioactive substances.